Geochemical composition of sediments in the Scheldt estuary with emphasis on trace metals

Superficial sediments of the Scheldt estuary were collected with a Van Veen grab at 57 stations between Temse and Vlissingen. They were analysed for major elements (Si, Al, Fe, Ca, Mg, Na, K, Cinorg and Corg) and trace metals (Cd, Pb, Cu, Zn, Cr, Ni, Co, Mn and Li). Factor analysis indicates that 44% of the variance can be explained by one factor which exhibits a high saturation for trace metals, organic matter, Al and Fe, all variables typical of fine mud. The high scores of this first factor are almost exclusively present in the upper estuary except for one area in front of Terneuzen. The second factor, which explains 23% of the variance, is typical of the carbonates and the third one (19% of the variance) is representative of the clay minerals. These two factors are more evenly distributed over the estuary. As usual, a strong influence of granulometry on the distribution of trace elements in the sediments was observed. Intercomparison of their composition within the Scheldt or with those of other aquatic systems requires thus a normalization procedure. This problem has been studied in detail by analysing various size fractions (63–16, 16–8, 8–4, <4 m) obtained by elutriation of the sample or by using a parameter characteristic of the fine fraction such as the concentration of a typical element (Al, Fe, Li, Corg). The normalization of trace metals allowed us to evaluate an enrichment factor of the trace elements in the estuarine deposits due to mans activities. In addition, it demonstrates the decrease of the anthropogenic impact on the composition of sediments by comparing the composition of sediments collected in 1976 and in 1994.     

Uptake of trace metals by sediments and suspended particulates: a review

This review addresses three of the possible mechanisms by which trace metals can be concentrated by sediments and suspended particulate matter. These are physico-chemical adsorption from the water column, biological uptake particularly by bacteria and algae, and the sedimentation and physical entrapment of enriched particulate matter. The relative importance of these three mechanisms will be different, depending upon the aqueous system, but there have been insufficient studies to allow the establishment of even rule-of-thumb guidelines, as yet, about their quantitative importance under different conditions.The importance of natural organic matter in the cycling of trace metals in aquatic systems has been stressed. This organic matter may complex with the trace metals and keep them in solution, or it may enhance the association of the trace metals with particulate matter by becoming adsorbed to the particulate surface and then complexing with the trace metals in the solution phase. Enhanced metal-particulate associations may also arise if the metal-organic complexes are able to adsorb to the surface.The behaviour of natural organic matter may be the single most important influence on trace metal cycling in aquatic systems and should receive considerably more attention in the future.     

The impact of food contaminants on the bioavailability of trace metals.

Organic solvents, detergents, organochloric compounds, pesticides, mycotoxins, residues of veterinary drugs and metals are examples for food contaminants; they are usually present at very low concentrations. Their impact on absorption and distribution kinetics of essential trace metals, if there is any, can be mediated by three types of mechanisms: 1. In animal experiments, contaminants like T-2 mycotoxins or 2,3,7,8 tetrachlorodibenzodioxin inhibited absorptive or excretory mechanisms at high concentrations which, however, are usually not found in food. 2. Food contaminants with metal binding properties can interact with essential metals in the intestinal lumen or during transfer through the intestinal mucosa and affect their absorption according to the rules of complex chemistry. To balance the effect of endogenous metal-binding food constituents, they should be present in comparably high quantities. Usually, however, the concentration of contaminants is approx. 6 orders of magnitude lower than that of endogenous food ligands. 3. Contaminating metals may interfere with the regulated absorption, distribution, and excretion kinetics of essential metals. Such mechanisms may be amplified by vicious cycles. In general, however, food contaminations with metals are too low to have an impact on the bioavailability of essential metals.     

Factors influencing the potential mobility and bioavailability of metals in dried lake sediments

Abstract

Samples taken from polluted creek sediments were dried at temperatures between 20°C and 100°C (either in air or under a nitrogen atmosphere) and selective chemical extraction procedures were then used to examine the effect of drying temperature and oxidation on the bonding mode distribution patterns of Zn, Pb, Cd and Cu. Exposure to air during the drying stage tended to increase the fraction of total metal which was less firmly bound (i.e. ion exchangeable, weakly sorbed). Less metal was present in these categories when higher drying temperatures were used, and temperature changes had a larger effect when the samples were dried under nitrogen. The drying process appears to promote metal migration to phases having a stronger bonding power. In most of the samples studied, heating caused Pb to migrate to the carbonate phase while accumulation in the organic/sulfide phases was the dominant process for Cu and Cd. In the case of Zn, migration to the carbonate phase was favoured in some studies (e.g. using air-dried samples), in other sediments the migration end-point was the organic/sulfide phases. During storage of dried samples at room temperature for prolonged periods (e.g. months) the amount of less firmly bound metal tended to increase, and nullified the distribution changes induced by drying. The effect was most pronounced in the case of Cd. The study highlights that significant errors in metal distribution pattern analyses can arise from sample preparation procedures and it has provided information on the possible mobilisation of metal when dredged sediment is land-dumped, i.e. allowed to dry in air.     

Distribution and bioavailability of heavy metals in different particle-size fractions of sediments in Taihu Lake,China

Abstract

Taihu Lake is one of the most important water sources in the economically developed central-eastern part of China, and metal pollution is a major concern for the lake. The distribution and bioavailability of Cd, Cr, Cu, Pb, Sb and Zn were analysed in undifferentiated bottom sediments and in various particle-size fractions of the sediment from different parts of the lake. The average concentration of total metals in undifferentiated sediments ranged from 0.86 mg kg^-1 (Cd) to 95.45 mg kg^-1 (Zn) for the entire lake, with the highest concentrations in Zhushan Bay. The concentration of heavy metals was higher in extremely fine sands (0.064–0.125 mm) and fine sands (0.125–0.25 mm) than in other fractions. Sequential extractions showed that Cu, Zn and Cd were the most bioavailable accounting for 55.6%, 38.7% and 30.0% of their total concentration, respectively. However, the bioavailable proportion of many metals was not significantly different between grain grades except for Cu and Zn, which were higher in silts (<0.064 mm) than in other grades. Compared with the background values of local soils, the concentration of Zn, Cd, Cu, Pb and Sb was higher, indicating enrichment in the sediment. From ecological safety concerns, Zn, Cd and Cu should be examined closely because of their higher bioavailabilty in the sediment.     

苍南海洋倾倒区沉积物中酸可挥发性硫化物与重金属的研究

为了更清楚认识倾倒区海域沉积物的污染状况,测定了苍南海洋倾倒区海域表层沉积物中酸可挥发性硫化物(AVS)、酸可提取重金属(SEM)的含量,并对AVS、SEM、及ΣSEM-AVS的平面分布进行分析.结果表明,该倾倒区表层沉积物中AVS含量为0.19-1.88μmol·g^-1,倾倒区附近海域AVS含量高于周边海域;SEM平均含量为2.4μmol·g^-1,SEM含量往倾倒区方向有增加趋势.从单个重金属对ΣSEM的贡献率来看,Zn>Cr>Cu>Pb>Cd,SEMZn基本在50%以上,而SEMCd均在1%以下,其分布形态主要受Zn的控制.ΣSEM-AVS差值均大于0,且在倾倒区及附近海域其ΣSEM-AVS值高于沿岸各站,说明倾倒区海域沉积物中重金属对生物可能有一定毒性,具有潜在重金属生态风险.     

Speciation and bioavailability of zinc in amended sediments

Abstract

The speciation and bioavailability of zinc (Zn) in smelter-contaminated sediments were investigated as a function of phosphate (apatite) and organic amendment loading rate. Zinc species identified in preamendment sediment were zinc hydroxide-like phases, sphalerite, and zinc sorbed to an iron oxide via X-ray adsorption near edge structure (XANES) spectroscopy. Four months after adding the amendments to the contaminated sediment, hopeite, a Zn phosphate mineral, was identified indicating phosphate was binding and sequestering available Zn and Zn pore water concentrations were decreased at levels of 90% or more. Laboratory experiments indicate organic amendments exhibit a limited effect and may hinder sequestration of pore water Zn when mixed with apatite. The acute toxicity of the sediment Zn was evaluated with Hyalella azteca, and bioaccumulation of Zn with Lumbriculus variegates. The survivability of H. azteca increased as a function of phosphate (apatite) loading rate. In contaminated sediment without apatite, no specimens of H. azteca survived. The bioaccumulation of Zn in L. variegates also followed a trend of decreased bioaccumulation with increased phosphate loading in the contaminated sediment. The research supports an association between Zn speciation and bioavailability.     

Dietary intake and bioavailability of trace elements

In order to assess the nutritional importance of trace elements, it is relevant to consider the factors regulating their metabolism. One of the most important factors is the true intake level. Conventional techniques such as diet history and interview studies in conjunction with standard food tables do not provide the true intake levels from prepared meals. Employing the duplicate portion technique, we have investigated the dietary intake of trace elements in prepared meals consumed by children, adults, and elderly in Sweden. The results indicate that the intake of potassium, magnesium, zinc, copper, and selenium is low when compared with the present recommended dietary allowance (RDA) values. It appears that a marginal deficiency of a number of trace elements may exist in the general population of affluent countries. When the dietary intakes are known, it is necessary to consider the bioavailability. This depends on the chemical form as well as the concentration of other dietary constituents such as fiber, phytate, carbohydrates, macrominerals, and vitamins in the diet. Knowledge of these interactions are important to improve the overall nutritional status of the population in general and patients in particuler.     

海南东寨港红树林沉积物中重金属的分布及其生物有效性

对东寨港红树林湿地沉积物中7种典型重金属元素(Cr、Ni、Cu、Zn、As、Cd 和Pb)的有效态含量和全量进行测定,并讨论了红树林湿地沉积物中重金属元素的分布特征及其生物有效性.结果表明： 7种重金属在东寨港红树林湿地的含量大于亚龙湾和三亚湾的红树林湿地,但与中国南方和世界各地的典型红树林湿地相比仍处于中等偏低水平.东寨港红树林湿地光滩、林缘、林内表层沉积物的重金属含量存在差异;在柱状沉积物中重金属伴随沉积明显,表现出较强的同源性.经EDTA萃取出的有效态金属在表层沉积物中含量依次为Cu＞Cr＞Zn＞Ni＞As＞Pb＞Cd;垂直梯度重金属有效态含量占总量的比例的最大值(除Ni外)均出现在表层或中上层;目标重金属元素有效态和总量在空间分布上具有明显正相关性,元素总量指标能较好地评估该元素的生物有效性     

Distribution,bioavailability, and potential risk assessment of the metals in tributary sediments of Three Gorges Reservoir: The impact of water impoundment

To investigate the impact of water impoundment on the metal contamination in sediments cores from the three tributaries of Three Gorges Reservoir (TGR), the concentrations, distribution, bioavailability, and potential risk of eight trace metals between summer and winter were analyzed using sequential analysis. The mean contents of all studied metals were higher than the geochemical background value, and were higher in summer than in winter. The results of the partitioning study indicated that Cr and Ni prevailed in the residual fraction, while a small proportion was found in the easily soluble fractions. Cu and Zn were distributed mainly in the residual and reducible fraction, while Cd and Pb were predominantly associated with non-residual fractions. These observations suggested that the most easily mobilized metals in the study area were Cd and Pb. The mean enrichment factors (EF) of Cu, Zn, Cd and Hg were higher than 1.5, revealing the potential anthropogenic inputs, whilst the EF of other metals remained within the range of natural variability. The positive correlation between non-residual Cu, Zn and Cd and their EF values further indicated that anthropogenic inputs were the potentially major contributor for the enrichment of Cu, Zn and Cd in TGR sediments. The results evaluated by both potential ecological risk index and modified risk assessment code (mRAC) of all sampling sites demonstrated the relatively high potential risk of sediment contamination effect in TGR.     

Ecotoxicity of trace metals for chironomids

The main issue of the present study was to evaluate Cd, Zn, Pb and Cu uptake in chironomid larvae and other freshwater benthic macro-invertebrates under field conditions. Secondly, laboratory experiments were performed to relate trace metal uptake in chironomid larvae with effects on growth and development, and to assess the fate of accumulated trace metals during metamorphosis or upon predation.     

Relationship of hydrogen bioavailability to chromate reduction in aquifer sediments

Biological Cr(VI) reduction was studied in anaerobic sediments from an aquifer in Norman, Okla. Microcosms containing sediment and mineral medium were amended with various electron donors to determine those most important for biological Cr(VI) reduction. Cr(VI) (about 340 microM) was reduced with endogenous substrates (no donor), or acetate was added. The addition of formate, hydrogen, and glucose stimulated Cr(VI) reduction compared with reduction in unamended controls. From these sediments, an anaerobic Cr(VI)-utilizing enrichment was obtained that was dependent upon hydrogen for both growth and Cr(VI) reduction. No methane was produced by the enrichment, which reduced about 750 microM Cr(VI) in less than six days. The dissolved hydrogen concentration was used as an indicator of the terminal electron accepting process occurring in the sediments. Microcosms with sediments, groundwater, and chromate metabolized hydrogen to a concentration below the detection limits of the mercury vapor gas chromatograph. In microcosms without chromate, the hydrogen concentration was about 8 nM, a concentration comparable to that under methanogenic conditions. When these microcosms were amended with 500 microM Cr(VI), the dissolved hydrogen concentration quickly fell below the detection limits. These results showed that the hydrogen concentration under chromate-reducing conditions became very low, as low as that reported under nitrate- and manganese-reducing conditions, a result consistent with the free energy changes for these reactions. The utilization of formate, lactate, hydrogen, and glucose as electron donors for Cr(VI) reduction indicates that increasing the availability of hydrogen results in a greater capacity for Cr(VI) reduction. This conclusion is supported by the existence of an enrichment dependent upon hydrogen for growth and Cr(VI) reduction.     

Temporal variations of trace metals in aquatic insects

1. Temporal fluctuations were measured in the concentrations of the trace metals cadmium (Cd), copper (Cu) and zinc (Zn) in six insect taxa collected from the same sites in a temperate zone lake over a 14-month period. The consequences of temporal changes in insect contaminant concentrations for biomonitoring studies are assessed. 2. Significant temporal fluctuations in the concentrations of the three metals were measured in almost all of the insect taxa studied. In no case was there a greater than sixfold change in the concentration of a trace metal over the course of the year. The extent of the fluctuations was generally greater for CD, a non-essential metal, than for the essential micronutrients Cu or Zn. 3. Temporal fluctuations in CD concentrations appeared to follow a seasonal periodicity for most taxa. Minima were measured during the winter period in the megalopteran Sialis spp. and in the dipteran taxa Chaoborus punctipennis, Glyptotendipes sp., and Procladius spp., whereas a maximum was measured in the mayfly Hexagenia Hmbata during the same season. In general, temporal fluctuations in Cu and Zn concentrations were less seasonal in character than were those of Cd. 4. For some of the taxon—metal combinations studied, temporal fluctuations in metal concentrations could be ignored in biomonitoring studies, whereas in other cases a temporal window of minimum variability should be chosen for the collection of organisms from different sites.     

蚯蚓对不同厚度复垦土壤中重金属生物有效性的影响

煤矸石充填复垦土壤理化状态和重金属水平能显著影响后续生态利用.为查明蚯蚓对矸石上不同厚度覆土中重金属(Cr、Cu、Pb和Zn)总量和有效态的影响,采用土柱实验,将蚯蚓接种到矸石上覆土,设置10、20、30、50、70 cm五种覆土厚度,通过测定不同厚度覆土pH、有机质(OM)、总氮(TN)、总磷(TP)、总钾(TK)和...     

施污土壤重金属有效态分布及生物有效性

以城市污泥为研究对象,将城市污泥与土壤按照一定的质量比配成污泥混合土壤.采用6种不同性质提取剂(0.05mol/L EDTA、0.1 mol/L CH3 COOH、0.01 mol/L CaC12、1 mol/L CH3COONH4,0.05 mol/L NaHCO3和0.05 mol/L Tris-HCl)分别对污泥混合土壤中重金属(Cd、Pb、Cu和Zn)的螯合态、酸溶态、中性交换态、中性结合态、碱性交换态和蛋白质结合态进行提取,考察污泥的添加对土壤中不同形态重金属的消长规律.通过黑麦草盆栽试验,探究污泥混合土壤中不同形态重金属的植物可利用性.结果表明:污泥混合土壤中重金属螯合态比例较大,占总量的20.3％-40.0％;其次为酸溶态和中性结合态,而中性交换态、碱性交换态和蛋白质结合态的含量较低.污泥的添加促进了黑麦草对Cd、Cu和Zn的吸收,在污泥添加率为44.4％时根部对其吸收量达最大,分别较CK处理增加了0.3、2.3和6.5倍.抑制了对Pb的吸收,在污泥添加率为37.5％时,根部对Pb的吸收较CK处理下降0.4倍.Pearson相关系数分析结果表明:污泥混合土壤中以螯合态、酸溶态和中性结合态存在重金属可被黑麦草吸收利用.     

Phosphorus bioavailability of fluvial sediments determined by algal assays

Eroding bank soils and riverine suspended sediments from the Flathead River-Lake ecosystem, Montana, USA, were cultured with the alga Selenastrum capricornutum Printz in PAAP medium with the sediments as the sole source of phosphorus. Extraction of phosphorus by NaOH and nitrilotriacetic acid (NTA) solutions were compared to results from algal bioassays. The fine sediment particles transported into Flathead Lake during spring runoff had the highest availability (i.e. 6% of total phosphorus). Bank soils which contained the greatest percentage of fine clays exhibited similar (i.e. 4% of total phosphorus) availability. Bank soils containing predominantly organic phosphorus had the lowest availability. Spearman's rank correlation indicated significance at the 5% test level between algal assay estimates of available phosphorus and both chemical extraction techniques.     

A kinetic approach to predict soil trace metal bioavailability: preliminary results

The presence of large amounts of trace metals creates a hazard in some soils that is strongly related to the speciation of these metals. The aim of this work was to apply an operationally defined fractionation based on kinetics, which could distinguish “labile” (quickly extracted) and “non-labile” (or slowly labile i.e. slowly extracted) cations by using the extraction kinetics of trace metals by EDTA. This kinetic fractionation was applied to 10 unpolluted soil samples from Burgundy (France) in order to determine their labile concentrations of lead and cadmium. According to this method, cadmium was found to be more mobile than lead, with respect to both labile concentration and the kinetic constants. Moreover, it was also found that the labile concentration of cadmium was related (R ²=0.6) to its concentration in wheat shoots; however, no such correlation was found for lead.     

Scandinavian limnochronology of sediments and heavy metals

Sediment and peat accumulation rates as well as heavy metal fluxes are examined in Scandinavian lakes, marine coasts and peatlands. Modern accumulation rates are determined using Pb-210 and other chronological tools. Mean deposition rates in the past 150 ± 20 yrs are 3–95, 40–190 and 1–5 mg·cm^–2·yr^–1 for lakes, marine coasts and peatlands respectively. The Pb-210 fluxes at the investigated sites are quite variable. The lowest values are found for peatlands 0.04–0.20 pCi·cm^–2·yr^–1 while coastal marine environments showed 0.35–0.70 pCi·cm^–2·yr^–1. A wide range of variation of Pb-210 fluxes is obtained for the studied lake sediments 0.01–0.51 pCi·cm^–2·yr^–1.The chronological records of Pb, Zn, Cu, Cd and Hg show that heavy metal fluxes are much higher in coastal marine areas. Inland lakes and ombrotrophic peat-bogs indicate that Pb is introduced exclusively through the atmosphere and decrease exponentially from South to North Scandinavia. However, the other heavy metals are transported to freshwater systems by different hydrologic and atmospheric processes. Zn and Fe exhibit some correlation with lake-drainage area.     

Vitellogenesis and trace metals in a marine teleost

The concentration and loss of copper and cadmium over the spawning period in relation to vitellogenesis in Blennius pholis L. and the implications for the viability of the developing embryo are described and discussed.